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Raising Cinnabar Moth Caterpillars

August 12, 2020

After 2 years of deliberately growing ragwort, I finally got my hands on 2 Cinnabar moth larvae! Unfortunately they did not come to my ragwort, but I managed to gather them from near by woodlands and used my garden plants to feed them until they pupated. 

Below I’ll give you some facts about the critters, a rundown of my experience and some (hopefully) helpful photos for anyone else who would like to observe the life cycle of the Cinnabar moth.

(I’m no expert, despite my blog exploding with people looking for butterfly advice every summer… I just really really really love watching bugs) 

Cinnabar moths only produce a single generation every year, so the window for collecting them as tiny larvae is pretty small and it occurs around the first or second week of July where I am in Scotland. 

The caterpillars are really easy to spot, particularly older ones because they are covered in black and yellow stripes and cluster together on their food plants boldly for protection. Their bright coloration serves as a warning to predators that they are not nice to eat as they store toxins from the ragwort they consume. They also have a couple of other food plants besides ragwort, but I’ve only ever spotted them on ragwort. 

If their food runs out the caterpillars are known to turn to cannibalism, however this is not something I’ve observed personally. 

When I spotted the caterpillars there were hundreds covering all the ragwort in the area, however they were quite large, and I wanted some smaller ones so that I could observe them for longer before they pupated. I removed two of the smallest I could find and transported them home in a plastic box kindly provided to me by my sister in law because I was completely unprepared despite being desperate to get my hands on these things for years and usually having a box in my bag for such an occasion. 

The two that I managed to acquire were in their third instar i believe, because I was only able to find evidence of a single molt (4th instar) before they pupated. 

Once home I transferred them into a large, clear plastic box for observation and provided them with plenty of ragwort leaves as well as ragwort flowers which they seem to love. (they also prefer the smaller younger leaves to the larger, older ones) 

At first they were very active but extremely shy. the second they noticed me watching them they would freeze up and would refuse to carry on until they felt suitably ignored. 

Their feeding was a bit odd in the beginning compared to other caterpillars I’ve observed as they would eat like mad, then go across to the other side of the box to be very still for a time followed by a bunch of poops… then they would go back to the food and repeat that over and over. After a couple days of this behavior they were ready to start preparing to shed their skins. Both retired to the top of the box for this task and it took them about a day of inactivity to shake off their old skins.

After the shed their eating behaviors became more in line with what I’ve observed in other caterpillars but actually a tiny bit more extreme as they ravenously ate and pooped in the same spot all day long. Sometimes creating hilarious pyramids of poo. The butterfly caterpillars I’ve raised (small cabbage white, large cabbage white and painted lady) tended to scatter their poops a lot more. Occasionally the cinnabar moth caterpillars made an effort to fling the poops, but mostly it was just big piles of it which i had to clear out regularly. 

At this point their bodies had also become much more vibrantly colored and the long white hairs that they have sticking out at all angles were easier to see. 

They ate this way for nearly a week, and I kept watching them to see if they shed their skins again but there was no pause in their behavior, or evidence of  the shed skins, so either they did it very quickly and ate the evidence, or they were on their fourth instar. 

Then one morning, all of a sudden they stopped eating and started running back and forth, all over the bottom of their enclosure. They had gotten quite large at this point and seemed to no longer be able to climb the sides without falling off halfway up. They ran like this for about a day, and I was getting quite worried until I realized that they were looking for a safe place to begin their next stage of life! (Google also confirmed they had reached their max size, 30mm)

Since they like to burrow before they pupate I provided their box with a bit of substrate and I put a dense clump of flowers on top as well as some twigs of dried leaves. 

Almost immediately after being put into their new enclosure one of the caterpillars burrowed into the substrate under the clump of flowers… it then came out and started laying silk. 

The species of butterfly caterpillars I’ve raised in previous years would lay silk almost constantly, however I noticed these moth caterpillars never did, so I knew I was definitely on the correct thought path  when I saw that this little guy was making his safe place. He strung the silk in the flower clump for about a day and then settled into the substrate underneath and went still. Then the next day the other caterpillar joined him about a centimetre away. 

It took roughly 3 days for both caterpillars to fully pupate, and now I have two lovely little bundles who will winter with us until next July when they will emerge as adult moths. The pupa is shiny and dark brown, tangled in the leftover flower twigs and silk. I flipped the dried flower bundle over to peek, but then returned it to the container slightly buried as that is how they settled in. Can only see half of one pupa, the other one is too cocooned in twigs and silk to see and I didn’t want to disturb it, so this is the best I can do for a photo. 

I hope that next year I can collect more of these because they were such a delight to observe and are so cute with their stripey roly poly bodies! My girls absolutely loved watching them as well. 

I’ve read that in the wild, not many of these caterpillars make it to adulthood because they have a tendency to strip their food plants so completely, then start eating each other.

If you would like to collect them from the wild for your own observation, first of all make sure that you have access to plenty of food for them and don’t take more than you can feed! Also make sure that if you have more than one you give them PLENTY of fresh food every day so they won’t run out when your back is turned and try to eat each other. 

Second, try to take ones from places where the food is scarcer to give the ones that are left behind their best chance for survival.

Third, never handle your caterpillars unless they are on a leaf, because that’s just safest for everyone involved.

Part of me is wishing I had taken more, but I wasn’t sure how long I would have them for or how much they would eat. Next year I will try again if I’ve got the ragwort to support them! 

Well that’s all I’ve got until next summer. I’ll update this blog entry when/if the moths emerge as that way all the information is in the same place. 

As ever, happy to answer any questions you may have to the best of my ability! :) 

 

From → Garden, Scotland

5 Comments
  1. Hello from Canada. I am raising local varieties of butterflies (I get eggs from the wild too) and I wanted to say how much I enjoy your posts. I put their food (the plant) in small jars with aluminum foil wrap over it and a hole in the middle also works. I am not as familiar with ragwort but I can’t imagine it would be too different. It helps drain away the poop, keep the food fresh and they can’t drown. Good luck with these and looking forward to seeing the update on these creatures next summer! My kids have also learned to appreciate insects more from raising these creatures. Thanks for sharing…

    • I forgot to say, I put water in the jars! With the aluminum foil over it, with a hole in the middle to stick the plant in. It keeps the plant food lasting longer. :-)

    • Thank you so much! Do you raise them on a large scale? I will definitely employ that tip in the future, next years caterpillars will definitely appreciate it :)

  2. Wend permalink

    Me again, I really need to catch up on most of your posts, I’ve been really poorly for the last few months, also just come out of shielding, its a whole new strange world to me now, so much to catch up on , thank you xx

  3. Wend permalink

    I must admit I was enthralled in this , to say I am actually afraid of moths and butterflies, but I actually cannot wait for them to emerge, and will be awaiting news on the little guys, good luck my friend xx

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